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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
    <script>
        var v;
        console.log(v);//undefined
        console.log(typeof(v));//undefined
        v = 3.14;
        console.log(v);//3.14
        console.log(typeof(v));//number
        v = 'js';
        console.log(v);//js
        console.log(typeof(v));//string
        v = true;
        console.log(v);//true
        console.log(typeof(v));//boolean
        v = null;
        console.log(v);//null
        console.log(typeof(v));//object

        var m = '3';
        var n = 3;
        if(m == n) {
            console.log('m==n');
        }

        if(m === n) {
            console.log('m===n');
        }
    </script>
</body>
</html>